Unanswered: Ext TreePanel: How to add Child Nodes to the expanded node ?

Unanswered: Ext TreePanel: How to add Child Nodes to the expanded node ?

Hi,I am trying to create a Tree from Ext.tree.Panel with JSON data.

My JSON{"employees": [{ "firstName":"John" , "lastName":"Doe" }, { "firstName":"Anna" , "lastName":"Smith" }, { "firstName":"Peter" , "lastName":"Jones" }]}
I want the first level nodes to be the "firstName: from the above JSON. I am able to achieve this but when any of the node is expanded the same nodes are displayed as children to the expanded node shown below.- John
---> + John---> + Anna
---> + Peter+ Anna
+ Peter

When any of the node is expanded I want to add children from another JSON file. but here the problem is before adding the children to the node i can see the child nodes attached as above.